feat: include per-descriptor code and limitName in response dynamic metadata

[sc0ttbeardsley]

Changes to dynamic metadata (RESPONSE_DYNAMIC_METADATA):

• Only built when at least one descriptor is over its limit (breaking change)
• Each descriptor now includes code (OK or OVER_LIMIT) from response status
• Each descriptor now includes limitName (matched limit name, if configured)

Before:

  {descriptors: [{entries: [key=val]}], domain: ...}

After (only when over limit):

  {descriptors: [{entries: [key=val], code: OVER_LIMIT, limitName: my-rule}], ...}